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To double spud production, just add a little spit

May 31, 2010  By Fruit & Vegetable


To double spud production, just add a little spit
When it comes to potentially doubling the output of the world’s fourth largest
food crop, the secret may be in the spit.

May 27, 2010, Ithaca, NY –
When it comes to potentially doubling the output of the world’s fourth largest
food crop, the secret may be in the spit.

Researchers at Cornell
, as well as the University of Goettingen and National University of
, have discovered that when a major South American pest infests potato
tubers, the plant produces bigger spuds.

The secret to this
increased yield, they write in the peer-reviewed journal Ecological Applications
(April 28, 2010), is found in the saliva of the Guatemalan potato moth larvae
(Tecia solanivora). The major pest, which forces many farmers to spray plants
with pesticides every two weeks, contains compounds in its foregut that elicit
a system-wide response in the Colombian Andes commercial potato plant (Solanum
) to produce larger tubers.

The researchers found that
when the spit of the tuber moth caterpillar gets into a tuber, all the other
tubers of the plant grow bigger, said co-author André Kessler, Cornell
assistant professor of ecology and evolutionary biology. Researchers believe
that compounds from the insect's saliva somehow increases the rate of the
plant’s photosynthesis to compensate for the tubers lost to the caterpillar damage.
As a result of more photosynthesis, more carbon is drawn into the plant and
used to create starch, which makes for bigger tubers.

Plants have a number of
responses to insects and other animals that eat them, including changing
metabolism or producing toxins, said Kessler. In turn, the herbivores may
develop strategies to counter the plant’s defenses and influence its signaling

“This could be an example
where the co-evolutionary arms race led to a beneficial outcome for both,” said

Another key seems to be
getting the right mix of potato and pest.

When the larvae infested
fewer than 10 per cent of the tubers, the plant produced marketable yields
(after infested tubers were removed) that weighed 2.5 times more than undamaged
plants, according to the study. When up to 20 per cent of the potatoes were
damaged, marketable yields still doubled. When as many as half of the potatoes
were infested, yields equaled those of plants with no infestation.

The findings have
implications for potato farmers. Once isolated, the compound could lead to
considerably higher yields in some varieties.

Initially, researchers
wanted to show how these pests reduced potato yields, but they actually they
found yield increases, said Katja Poveda, the study’s principal investigator,
at the Agroecology Institute of the University of Goettingen, Germany, and the
Cornell entomology department.

“The moth eats all varieties of potatoes, but so far only
this one variety responded” with increased yields among seven varieties that
were tested as part of a larger project, said Poveda. Future experiments will
test more commercial varieties, as well as wild potatoes, she added.

The study can be found
online at

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